Electrostatic latent image developing apparatus

ABSTRACT

Apparatus for developing an electrostatic latent image wherein a developing tray is located in a developing chamber, said tray adapted to receive sensitized paper for developing. A supply pipe having a pump therein discharges developing solution onto said tray, said supply pipe receiving the solution from a supply chamber which includes carrier liquid at the other end to the developing chamber. A particle container is connected with said return pipe and contains image-producing particles that are charged by an electrode in the nozzle as they pass into the carrier liquid. A concentrate indicator in the return pipe regulates a valve arrangement to allow the particles to pass into the return pipe and be added to the carrier liquid.

United States Patent ELECTROSTATIC LATENT IMAGE DEVELOPING APPARATUS 3 Claims, 8 Drawing Figs.

US. Cl 1 18/637, 117/37, 252/62.l

Int. Cl 1305b 5/02 Field of Search 118/637,

Primary Examiner-Peter Feldman Attorney-Burgess, Ryan and Hicks ABSTRACT: Apparatus for developing an electrostatic latent image wherein a developing tray is located in a developing chamber, said tray adapted to receive sensitized paper for developing. A supply pipe having a pump therein discharges developing solution onto said tray, said supply pipe receiving the solution from a supply chamber which includes carrier liquid at the other end to the developing chamber. A particle container is connected with said return pipe and contains image-producing particles that are charged by an electrode in the nozzle as they pass into the can-ier liquid. A concentrate indicator in the return pipe regulates a valve arrangement to allow the particles to pass into the return pipe and be added to the carrier liquid.

ELECTROSTATIC LATENT IMAGE DEVELOPING APPARATUS BACKGROUND OF THE INVENTION The present invention relates to electrostatic latent image developing apparatus.

The conventional developing solution used for wet developing an electrostatic latent image is a solution consisting of a carrier liquid having a high electric resistance sufficient enough to prevent the destruction of an electrostatic latent image, a pigment suspended in a carrier liquid and a control agent coating the pigment so as to render it electrically selectable by the electrostatic latent image charge, and the control agent serves to control the charge upon the pigment. Such developing solution in which are suspended in the carrier liquid the pigment and the control agent for controlling the charge upon the pigment is applied to a recording body having thereupon an electrostatic latent image so that a visible image is produced upon the electrostatic latent image by the electrophoretic method.

However, in the conventional developing solution of the type described above, there are the following defects: (1) the substances used as a control agent are limited to an extremely less extent and are effective only in a limited number of combinations with a carrier liquid; (2) since the control of the charge by the control agent is based upon the electrochemical property thereof, the chemical absorption in the thermal equilibrium state between the pigment and the control agent varies due to the temperature change of the carrier liquid so that the control becomes unstable, thereby causing instability of the polarity of the charge attached to the pigment particle; (3) when impurities, especially polarizable substance such as water, alcohol, surface active agents, etc. are mixed into the carrier liquid, the control of the charge upon the pigment particle by the control agent becomes unstable or the control power is reduced or lost so that the control agent can not function as it should do; and (4) when the substance constituting the recording body such as synthetic resins, conductivity imparting agents, etc. are dissolved into the carrier liquid by this liquid upon contact therewith, the chemical composition of the developing solution varies so that the control of the charge upon the pigment particle becomes unstable or the suspension of the pigment particles is deteriorated, whereby the developing process can not be effected as desired.

In view of the above one of the objects of the present invention is to provide apparatus for preparation of developing solution of the type described in which the above described defects encountered in the conventional developing solution can be completely eliminated and apparatus method for developing an electrostatic latent image which can be directly coupled with the developing solution preparation apparatus of the present invention.

SUMMARY OF THE INVENTION According to the present invention, the developing solution is a mixture of a liquid having a high electric resistance sufficient enough to prevent the destruction of an electrostatic latent image upon a recording body and image-producing particles which have been charged by a pair of electrodes between which is applied a potential. The prepared developing miution may be applied to the surface of the recording body having thereupon the electrostatic latent image so that charged image-producing particles are caused to settle down to the surface of the recording body along line of electric force produced by the charge forming the electrostatic latent image, thereby visualizing the electrostatic latent image.

The above described charge image-producing particles are charged artificially by a high-tension so that the method of the present invention is quite different from the conventional method in which the charge of the particles is controlled by the control agent. The present invention has an advantage that the charge and the polarity of the image-producing particle may be suitably determined by determining suitable voltage and polarity applied to the electrode which contacts the image-producing particles. The present invention is not utilizing the electrochemical property of the substance such as a control agent for charging the particles so that it will be clear that the charged condition of the image producing particles remains unchanged due to the temperature change of the liquid into which are mixed the charged image-producing particles and due to the mixture of impurities into the liquid. Therefore, an excellent stable developing solution may be obtained.

The liquid into which are mixed the charged image-producing particles must have a high electric resistance sufficient enough to prevent the deterioration of an electrostatic latent image and a high electric resistance and a low dielectric constant sufficient to prevent the dissipation of the charge of the image-producing particles at least while the recording body having thereupon the electrostatic latent image is being developed. Preferably, the liquid has a specific resistance of the order higher than 10 ohm-cm. and a dielectric constant less than 3. For example, paraffin hydrocarbons, aromatic hydrocarbons, mixtures of aromatic hydrocarbons, aliphatic hydrocarbons, halogenated hydrocarbons, etc. be used as a carrier liquid. But it is to be understood that the liquid used in the present invention is not limited to the above described liquids, but other liquids whose properties satisfy the above described conditions may be also used. Furthermore, the mixtures of one of the above described liquids and natural high molecular compounds or synthetic high molecular compounds which can be dissolved into said liquid can be also used as a carrier liquid as long as such mixtures satisfy the above described conditions.

As to the charged image-producing particles, pulverized compounds are provided which can be charged by electrodes to which is applied a relatively high potential. For example, the compounds which can be used as image-producing particles are conductive compounds, nonconductive compounds (insulating compounds). semiconductor compounds, etc. and more particularly various metallic powder and carbon powder as conductive compounds. More specifically, black gold particles called gold black," black silver particles called silver black, black carbon pigment particles called carbon black," metallic aluminum powder particles and other metallic powder may be used. As nonconductive and semiconductor compounds, metallic oxides, powder of single elements having a semiconductor property such as sulfur powder, selenium powder, silicon powder, etc. organic pigment powder, inorganic pigment powder, natural and synthetic resin powder, natural and synthetic high molecular compound powder, etc. may be used. The compounds which are used as imageproducing particles are not limited to those described above, but any other compound as far as they can be charged by application of a potential may be used as image-producing particles in the present invention. Furthermore, it is not required to use as image-producing particles only one of the compounds as described above, but any combination of them can be ad vantageously used. For example, mixtures of metallic powder with natural or synthetic resins; and metallic or nonmetallic powder coated with natural or synthetic resins or high 'molecular compounds may be used. Any colorants such as dyes in order to color image-producing particles to the recording bodies may be selected freely as far as the properties of imageproducing particles which are charged by a high potential are not lest by addition of these agents. As to the particle sizes of image-producing particles, principally the particle sizes are not limited at all, but in view of the formation of an image over the recording body and the floating characteristics of the image-producing particles mixed in a carrier liquid, it is preferable that the size is less than 50p.

Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments thereof, taken in conjunction with the accompanying drawing.

BRIEF DESCRllPTl'ON OF THE DRAWINGS FIGS. 1 to 4 are schematic sectional views each illustrating a different embodiment of a device used in preparation of developing solution according to he present invention;

FIG. 5A and B are sectional views illustrating nozzles used for issuing image-producing particles in the above development solution preparation devices;

FIG. 6 is an sectional view of one portion of a image producing particle transporting pipe illustrating a screenshaped electrode interposed therein; and

FIG. 7 is a sectional view of one embodiment of a developing device of the present invention.

DESCRIPTION OF THE PREFERRED EMBODlMENT According to the present invention, the developing solution is prepared by, prior to or after mixing the image-producing particles of the type described above into the carrier liquid of the type described above, applying a potential to said imageproducing particles so as to charge them. The method of the preparation of the developing solution and the device for developing latent images by using said developing solution of the present invention will be described hereinafter in more detail with reference to the accompanying drawing. Referring to FIG. 1, a blower 2 is disposed in a container in which is disposed powder 1 consisting of image-producing particles. The powder ll mixed with the air which is introduced into a transportation pipe 4 by disposed above a carrier liquid chamber 6 and is provided with an electrode 7 in the form of a nozzle. The electrode 7 may be directly attached to the pipe 4 when the latter is made of an insulating material while when the pipe 4 is made of a conductive material, the electrode 7 is attached to the pipe through a suitable insulating body ii. A potential is applied between the electrode 7 and an opposing electrode 9 which is disposed in the liquid chamber 6 made of an insulating material. On the other hand, when the carrier liquid chamber 6 is made of a conductive material, the liquid chamber 6 itself may be used as an opposing electrode 9. Since the potential applied therebetween is relatively high, it is preferable to make the carrier liquid chamber from the insulating material in view of safeguarding the operation.

When it is desired to charge the image-producing particles with a positive charge, the electrode 7 is applied with a positive potential while when it is desired to charge the image producing particles with negative charge, the electrode 7 is applied with a negative potential. While a positive or negative potential is applied to the electrode 7, the image-producing particles are made to pass through the electrode together with the air and theredter mixed with the carrier liquid lltl, whereby the developing solution containing the charged image-producing particles is prepared.

Example Aluminum powder was used as the image-producing particles and refined white kerosene was used as the carrier liquid. The diameter of the nozzle 7 made of the electrode was approximately 0.5 mm; the distance between the nozzle 7 and the electrode 9, approximately 200 mm; the issuing speed of the image-producing particles from the nozzle, approximately 1 m./sec.; and the potential applied to the nozzle,+2,000 v. The developing solution was prepared from the above materials under the above conditions. A photoconductive material consisting of a mixture of resin and zinc oxide was applied to the base so that the electrostatic photocopying paper was prepared. Upon this paper was formed a negatively charged electrostatic latent image and the above developing solution was applied to this electrostatic latent image in the dark room. Then, the positive having an excellent metallic silver luster was obtained. Since the positive image was composed of aluminum powder, aluminum powder tends to separate from the photocopying sheet under the light so that a transparent vinyl resin coating was applied thereupon by aerosol or spraying method, whereby the positive image having metallic silver luster which can be recorded was obtained.

According to another embodiment of the present invention, a better developing solution may be obtained by first mixing the image-producing particles with the carrier liquid, and then passing the liquid containing the image-producing particles through the electrode nozzle. ln H6. 2, the image-producing particles 21 mixed with a liquid equivalent to the carrier liquid in a carrier liquid chamber 26 are stored in a container which is intercommunicated with a transporting pipe 24 through a fine diameter tube 24a. When air is blown toward a nozzleshaped electrode 27 disposed at the open end of the pipe 24 by means of a blower 22 interposed in the pipe 24, the imageproducing particles 21 are sucked through the fine diameter tube 24a into the transporting pipe 24 by the negative pressure produced at the upper end of the fine diameter tube 240, and are finally ejected through the electrode nozzle 27. When a potential is applied between the nozzle electrode 27 and an opposing electrode 29, the image-producing particles passing through the electrode nozzle are charged as the same polarity with that of the nozzle electrode 27, and the charged imageproducing particles are mixed into the liquid 20 whereby the developing solution can be prepared.

Example Carbon black was used as the image-producing particles and was mixed into an aromatic hydrocarbon, that in toluol. The mixture was ejected from the nozzle made of the electrode 27 having the diameter of approximately 0.3 mm. The issuing velocity could not be measured accurately, but is was observed that the spray was similar to those produced by ordinary spraying. In the carrier liquid chamber 26 was contained a polyhalogenated derivative of hydrocarbon, that is freon. The mixture was made to pass through the nozzle to which was applied a potential of +l,000 v. and further mixed with the carrier liquid. The distance between the electrode 27 and the opposing electrode 29 was 200 mm. The prepared developing solution was applied to the electrostatic latent image produced upon the electrostatic photocopying paper in the dark room and the excellently sharp positive was obtained. Alternatively, the electrode 27 was applied with a potential of -5,000 v. with other conditions remaining unchanged in order to prepare the developing solution. The obtained developing solution was applied in the same manner as described above and the reversed image, that is the negative having more or less edge effect was obtained. Furthermore, pulverized acrylic resin colored with red, yellow, blue and green was mixed into the mixture of refined white kerosene and approximately 15 percent toluol. The mixture was made to pass through the electrode nozzle to which was applied a potential of +5,000 v. and mixed into the carrier liquid of refined white kerosene, whereby the developing solution was prepared. The electro static photocopying paper having a negatively charged electrostatic latent image was immersed into this developing solution, so that the positive colored with the above described colors was obtained. The positive is naturally fixed to the paper as the developing solution dries so that the paper can be recorded without any further image fixing process.

The third embodiment of the present invention will be described hereinafter with reference to FIG. 3. The noncharged image-producing particles are mixed in a carrier liquid 331 which is circulated through a transportation pipe 34. When the carrier liquid is ejected through an electrode 37 which is made into the form of a nozzle, the image-producing particles are charged continuously by a potential applied between the electrode 37 and an opposing electrode 39. When this operation is continued, the developing solution containing the charged image-producing particles can be prepared. in FlG. 3, reference numeral 32 designates a liquid circulating pump interposed in the transportation pipe 34.

According to the fourth embodiment of the present invention, as shown in FIG. 41, a nozzle $7 from which are issued image-producing particles or liquid containing these particles is immersed in a carrier liquid 40 and a potential is applied between the electrode, that is the nozzle $7, and an opposing electrode plate 49, so that the developing solution having the same effects as those of the developing solution described above can be prepared.

As to a nozzle which is used as an electrode, a nozzle having only one hole, a nozzle in which are assembled a plurality of relatively fine diameter tubes as shown in FIG. 5A or a nozzle in which conductive fibers are packed in the nozzle as shown in FIG. 5B may be used.

FIG. 6 illustrates a device wherein instead of a nozzle which is used as an electrode, a screen-shaped electrode 67 is interposed in a transporting pipe 64 and a potential is applied to this screen-shaped electrode 67 and an opposing electrode disposed within a carrier liquid chamber, whereby the imageproducing particles passing through the screen-shaped electrode are charged.

In addition to the use of the nozzles and the screen-shaped electrode interposed in a transporting pipe for obtaining charged image-producing particles, a portion of a liquid circulating pump, for example, a rotor, may be advantageously used as an electrode when the circulating pump is interposed in the transporting pipe for circulating the developing solutron.

It is preferable that an insulating layer is applied to the carrier liquid chamber when the chamber is used as an opposing electrode or to the opposing electrode within the chamber made from an insulating material so that the direct contact of the charged image-producing particles with the chamber or the opposing electrode may be prevented, thereby prolonging the lift of the charged particles as long as possible.

FIG. 7 illustrates schematically apparatus for developing a electrostatic latent image produced upon an electrostatic photocopying paper by applying the developing solution prepared by one of the methods described above. A developing solution 70 is discharged into a developing tray 85 located in chamber 90 through a supply pipe 84 by means of a circulating pump 82. A guide plate 86 made from a conductive screen is disposed upwardly of the developing solution tray 85 and a paper 87 having an electrostatic latent image is made to pass between the tray 85 and the guide plate 86 by means of a pair of feed rollers 88 and 89, whereby the paper 87 is developed while it passes through the developing solution. The developed paper is discharged out of the tray by suitable means not shown. The developing solution overflowing from the tray 85 is returned to the carrier liquid chamber 79 through a transportation pipe 74 intercommunicated with the chamber 90 and through a nozzle 77. Reference numeral 72 designates a circulation pump for returning the developing solution; 91, an instrument for detecting the concentration of the developing solution; 92, auxiliary image-producing particles; and 93, a valve which is used to add a suitable quantity of auxiliary image-producing particles into the transporting pipe 74. The valve 93 may be actuated manually or automatically in response to the decrease of the concentration of the developing solution, that is when the quantity of imageproducing particles per unit volume of the carrier liquid is decreased, so that a suitable amount of image-producing particles may be added into the carrier liquid. In case of the automatic supply, the valve 93 may be interlocked with the detecting instrument 91.

The present invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the present invention as described hereinabove and as defined in the appended claims.

I claim:

1. Electrostatic latent image developing apparatus comprising:

a developing chamber;

a developing tray located within said chamber and adapted to receive a sensitized paper having a latent image thereon to be developed;

a supply container separate from said developing chamber for storing carrier liquid;

a supply pipe having an inlet end immersed in said carrier liquid and having an outlet end connected with said developing chamber, said supply pipe having a pump therein to discharge developing solution into said developing chamber above said tray;

a return pipe connected at one end to the bottom of said developing chamber, said return pipe extending around and above said supply container and having the other end positioned within said supply container, said return pipe having a pump therein to discharge developing solution into said supply container;

a particle container positioned above the extended part of said return pipe and connected thereto by a valve connection, said valve connection selectively operable to allow image-producing particles located in said particle container to pass into said return pipe to be added to the carrier liquid;

a concentration indicator located in said return pipe to determine said selective operation of said valve connection; and

an electrode mounted on said other end of said return pipe so that an electrical potential applied thereto will apply a charge to said particles passing into the carrier liquid to form the developing solution.

2. Apparatus according to claim 1, in which the other end of said return pipe is formed as a nozzle having said electrode mounted therein.

3. Apparatus according to claim 2, in which said nozzle is immersed in the carrier liquid, and the electrical potential is connected between said electrode mounted therein and the supply container. 

2. Apparatus according to claim 1, in which the other end of said return pipe is formed as a nozzle having said electrode mounted therein.
 3. Apparatus according to claim 2, in which said nozzle is immersed in the carrier liquid, and the electrical potential is connected between said electrode mounted therein and the supply container. 